Magnetic coupling and method for calibrating a robotic system

Abstract

An apparatus for calibration of a robotic arm having an end effector of a robot includes a magnetic coupler having a body, a receiving face, a mounting member, and a magnetic portion. The mounting member is configured to fixedly connect to the end effector of the robotic arm. A mechanical digitizer probe having a ball and a handle are provided, where the ball is fixedly attached to a distal end of the handle and the ball is removably coupled to the magnetic coupler via the magnetic portion on the receiving face to form a rotatable ball and socket connection, and where a proximal end of the handle is adapted to be attached to a mechanical digitizer associated with the robot. A method for calibration of the robotic arm of a robot is also detailed.

The invention claimed is: 
     
       1. An apparatus for coupling a digitizer to a robotic arm having an end-effector for facilitating the calibration of the robotic arm, the apparatus comprising:
 a first coupler comprising a mounting member and a receiving member; and 
 a probe comprising a curved surface and a second coupler, wherein the curved surface is configured to couple to the receiving member and rotate relative to the receiving member as the robotic arm moves the end effector; and 
 wherein the mounting member is configured to couple to the end-effector of the robotic arm, and the second coupler is configured to couple to a distal end of the digitizer. 
 
     
     
       2. The apparatus of  claim 1  wherein the curved surface magnetically couples to the receiving member. 
     
     
       3. The apparatus of  claim 1  wherein the mounting member comprises a plurality of intrusions to align the first coupler in a specific orientation on the end effector. 
     
     
       4. The apparatus of  claim 1  wherein the first coupler further comprises a plurality of supporting members extending from said receiving member. 
     
     
       5. The apparatus of  claim 1  wherein the first coupler further comprises at least one rotation bearing, wherein said at least one rotation bearing permits the receiving member to rotate relative to the mounting member. 
     
     
       6. The apparatus of  claim 4  wherein at least one supporting member of said plurality of supporting members comprises a second bearing. 
     
     
       7. A method for calibrating a robotic arm of a robot, said method comprising:
 manipulating a robotic arm to a plurality of calibration locations, wherein a digitizer is coupled to an end-effector of the robotic arm with the apparatus of  claim 1 ; 
 recording joint values of the robotic arm at each calibration location; 
 measuring, with said digitizer, a spatial position with respect to the end effector at each calibration location; 
 identifying kinematic parameters of the robotic arm with a calibration algorithm utilizing the recorded joint values and the measured spatial position at each calibration location; and 
 implementing the kinematic parameters to complete the calibration of the robotic arm. 
 
     
     
       8. The method of  claim 7  further comprising determining multiple sets of joint commands, wherein each set of joint commands specify a calibration location for said end-effector. 
     
     
       9. The method of  claim 8  wherein the measured spatial position with respect to the end-effector is a shared point between said robotic arm and said digitizer, wherein each spatial position is measured and recorded relative to a coordinate system of said mechanical digitizer, and wherein one or more computers records the joint values of the robotic arm in a coordinate system of said robotic arm. 
     
     
       10. The method of  claim 9  wherein the calibration algorithm further determines a coordinate transformation between the coordinate system of the digitizer and the coordinate system of the robotic arm. 
     
     
       11. The method of  claim 10  wherein the calibration algorithm is based on at least one of linear least-squares parameter estimation, nonlinear least-squares estimation, optimization, or Kalman Filtering. 
     
     
       12. The method of  claim 10  wherein the coordinate transformation is determined by modeling the digitizer as one or more extra links of the robotic arm. 
     
     
       13. A robotic system, comprising:
 a robotic arm for moving an end-effector to a plurality of end-effector locations; 
 a digitizer; 
 the apparatus of  claim 1  for coupling the end-effector and the digitizer; and 
 a computer for receiving position data from the digitizer, the position data corresponding to a spatial position with respect to the end-effector at each of the plurality of end-effector locations. 
 
     
     
       14. The robotic system of  claim 13  wherein the one or more computers receive joint values of the robotic arm at each of the plurality of end-effector locations. 
     
     
       15. The robotic system of  claim 14  wherein the computer executes a calibration algorithm to determine kinematic parameters of the robotic arm using the position data from the digitizer and the joint values of the robotic arm. 
     
     
       16. The robotic system of  claim 13  wherein the spatial position of the end-effector is a shared point between the digitizer and the robotic arm. 
     
     
       17. The robotic system of  claim 13  wherein the curved surface magnetically couples to the receiving member. 
     
     
       18. The system of  claim 13  wherein the first coupler further comprises at least one rotation bearing, wherein said at least one rotation bearing permits the receiving member to rotate relative to the mounting member.